Killer asteroid hunter suffers from poor vision

The first of the asteroid-hunting Pan-STARRS telescopes will be taken apart today in an effort to solve problems with image quality.

The 1.8-metre PS1 telescope is the first of a suite of instruments – the Panoramic Survey Telescope and Rapid Response System – designed to find asteroids and comets with orbits that could bring them close to Earth. Sited atop a volcano on the Hawaiian island of Maui, PS1 is the prototype for a planned four telescopes that will image the whole sky visible from Hawaii three times each month.

To scan so much sky, PS1 boasts a 1.4-billion-pixel digital camera and specially designed software to process the terabytes of data collected by the telescope each night.

But since the camera was installed in 2007, the telescope team has been struggling to get PS1’s image quality to its targeted level. “There have been problems that we just didn’t anticipate,” says Pan-STARRS principal investigator Nick Kaiser of the University of Hawaii at Manoa.

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Big bananas

PS1’s first problem was a misalignment of the optics. “When we switched the telescope on two years ago we had terrible-looking images. We could get sort-of round stars in the middle of the field, but they were big and fuzzy. But the stars at ends of the field looked like telephone handles or big bananas,” Kaiser told New Scientist.

That problem was quickly fixed, but the images PS1 is taking are still 40 to 50 per cent fuzzier than they are supposed to be. “We’re spending half our time doing mediocre science and half our time trying to improve it so we can do great science,” says PS1’s director, Ken Chambers, a colleague of Kaiser at Manoa.

The main culprit now seems to be a set of joints connected to the 18 rods that hold up the telescope’s secondary mirror. These joints help connect the mirror to motors that adjust the mirror to counteract distortions of the telescope, which expands and contracts due to temperature changes and sags slightly as it scans across the sky.

The minute adjustments of the mirror are not occurring as they should be owing to a flaw in the original design, says Kaiser. So a crew will remove the secondary mirror to replace the joints and make other improvements to the support structure. The telescope is expected to be offline for several weeks, but if all goes well the procedure should go a long way toward improving the telescope’s image quality.

High hopes

The US air force has invested some &dollar;60 million in Pan-STARRS for research and development and to build PS1. A second telescope is now under construction.

Kaiser says the team hopes to run PS1 for three-and-a-half years on the summit of the Haleakala volcano in Maui, then move it to Mauna Kea on the island of Hawaii in 2012 to join three other Pan-STARRS telescopes.

When complete, Pan-STARRS should be able to detect objects 100 times fainter than those spotted by current surveys, including 99 per cent of any asteroids 300 metres across or larger that come near Earth’s orbit. The data will also be used for other investigations, ranging from the stellar structure of the Milky Way to the effects of dark energy.